The generalist fungal pathogen Pyrenophora semeniperda
occurs primarily in cheatgrass (Bromus tectorum) seed
banks, where it causes high mortality. We investigated the relationship
between this pathogen and its cheatgrass host in the context
of fire, asking whether burning would facilitate host escape
from the pathogen or increase host vulnerability. We used a series
of laboratory and field experiments to address the ability of
host seeds and pathogen life stages to survive fire. First, we
determined the thermal death point (TDP50; temperature causing
50% mortality) of seeds and pathogen propagules at two time intervals
using a muffle furnace. We then measured peak fire temperatures
in prescribed burns at sites in Utah and Washington and quantified
seed and fungal propagule survival using pre- and postburn seed
bank sampling and inoculum bioassays. Finally, we investigated
the survival of both seeds and pathogen after wildfires. We found
that radiant heat generated by both prescribed and wild cheatgrass
monoculture fires was generally not sufficient to kill either
host seeds or pathogen propagules; most mortality was apparently
due to direct consumption by flames. The 5-min mean TDP50 was
164ºC for pathogen propagules and 148ºC for host seeds,
indicating that the pathogen is more likely to survive fire than
the seeds. Peak fire temperature at the surface in the prescribed
burns averaged 130ºC. Fire directly consumed 85-98% of the
viable seed bank, but prescribed burns and wildfires generally
did not lead to dramatic reductions in pathogen inoculum loads.
We conclude that the net effect of fire on this pathosystem is
not large. Rapid postburn recovery of both host and associated
pathogen populations is the predicted outcome. Postfire management
of residual cheatgrass seed banks should be facilitated by the
persistent presence of this seed bank pathogen.